Various systems have been developed to steer a machine. One well known system is a rack and pinion system found in passenger vehicles. However, rack and pinion systems are not well suited for heavy machinery such as skidders, front loaders, scrapers, or articulated trucks. In these applications, the steered wheels may become ineffective in the soft earth. Articulated machines have been used as an alternative steering system.
Articulated machines have a front frame member, a rear frame member, and an articulation joint connecting the front and rear frame members. Typically, to steer an articulated machine, the front frame member must be rotated relative to the longitudinal axis of the rear frame member about the articulation joint while the machine is being propelled.
To rotate the front frame member, these machines commonly include articulation cylinders mounted between the frame members. The articulation cylinders are operated in opposite directions. That is, when one cylinder is extended forward, the other cylinder is retracted rearward and vice versa causing the front of the machine to face the intended turn.
Articulated machines are typically propelled by an internal combustion engine that drives the machine's wheels through a transmission, driveshaft, and differential. The machine is turned when the engine drives the wheels with the machine articulated by the hydraulic cylinders.
Prior alternatives have been developed to the prior articulated machine steering system described above. One such example is a machine utilizing skid steering. Skid steering machines are steered by driving the wheels on one side of the machine at a different rate of speed or direction than the wheels on the other side. For example, in such a steering system, the front wheels are not permitted to pivot relative to the rear wheels. As a result, several of the wheels are dragged, or "skidded," as the machine makes its turn since all of the wheels are not rotating at the same speed. Because the wheels are dragged, skid steering is typically limited to machines having a short wheel base and/or light weight.
Thus, it is desirable to provide an improved steering system for an articulated machine that overcomes the shortcomings of the prior art. The present invention is directed to overcoming one or more of the problems as set forth above.